Everyone in Zimbabwe knows the story of her shooting down an enemy helicopter in her country’s war of liberation. Spill Blood was her nom de guerre.

She married an even more famous freedom fighter, and the couple became political royalty after independence in 1980. She considered herself to be like a daughter of the only leader Zimbabwe has known, Robert Mugabe. She served as a vice president and was destined, it seemed, to succeed him.

But perhaps she and her husband, Solomon, were a little too eager for a succession. He was killed in 2011 in a mysterious fire that Ms. Mujuru now says was an assassination by forces loyal to the president. The president’s increasingly powerful wife, Grace, rushed to the Mujurus’ palatial estate to offer her condolences — in a way that heightened Ms. Mujuru’s suspicions.

“Instead of showing she had come to mourn, she was now busy admiring the house,” Ms. Mujuru said.

The president’s wife eventually led a purge of Ms. Mujuru from the governing party, accusing her of plotting a coup, performing witchcraft and wearing miniskirts.

“Even my own mother came to ask me, ‘When did you start practicing those things?’” she said.

Now, after staying out of the public light for more than a year, Ms. Mujuru, 60, is back, immersed in a widening political battle as the end of an era dominated by Mr. Mugabe looms over the country.

After ruling Zimbabwe, outwitting his opponents and crushing his rivals for decades, Mr. Mugabe, 92, is increasingly weakened by age. Political maneuvering has split his long-dominant ZANU-PF party, as factions jostle for control once the leader keeping them together dies.

Amid the uncertainty, Ms. Mujuru sees a political opening, vowing to take power as president in the 2018 election under the banner of her own party, Zimbabwe People First.

On a recent afternoon, Ms. Mujuru greeted a stream of visitors to her home, mostly allies who had been expelled along with her from Mr. Mugabe’s party, some with military ties.

Considered a moderate while in Mr. Mugabe’s circle, she presents the biggest challenge yet to the governing party from a former insider.

“For the first time, we have people who were in government and in the ruling party now outside and in large numbers,” said Jonathan Moyo, the minister of higher education and one of ZANU-PF’s most influential officials. “We have many of them to make a school. I don’t know whether they will make a political party. But it is a new challenge for us, yes.”

There are strong indications that Mr. Mugabe’s party, currently split in two, is taking the threat from Ms. Mujuru seriously. Mr. Mugabe has recently attacked the Mujurus at public rallies. Ms. Mujuru’s supporters have become the most frequent target of physical assaults by the president’s loyalists in rural areas, according to human rights organizations.

And ZANU-PF officials now even dismiss as “a lie” Ms. Mujuru’s celebrated claim of shooting down that helicopter decades ago.

“People are now trying to rewrite history,” she said.

As Ms. Mujuru tells it, helicopter gunships belonging to the former Rhodesian government appeared near her village in the country’s northeast one day in February 1974 as she and others were looking for fresh recruits. With her father’s approval, she had joined the liberation movement a few months earlier after finishing the ninth grade.

“As they were trying to take a turn,” she recalled of the helicopters, “this other comrade who was injured, whom I didn’t want to leave, then told me just to shoot.”

“I was surprised when it went down,” she added.

Whether her shots brought down the helicopter or not, the story of Spill Blood’s heroism quickly spread. She rapidly rose to become one of the first female commanders in the liberation army and, in 1977, married one of its top leaders, Solomon Mujuru.

Mr. Mujuru played a pivotal role in helping Mr. Mugabe — an intellectual who had spent a decade in prison and was held in suspicion by other rebel commanders — rise to become the movement’s political leader.

Upon independence in 1980, Mr. Mugabe named Mr. Mujuru army chief and made Ms. Mujuru the youngest minister in his first cabinet. The husband went into business and became one of the country’s richest men.

He played the role of kingmaker in politics and successfully pushed for his wife to become a vice president in 2004. To many, the Mujurus had set the stage for a succession.

Mr. Mugabe, too, had taken notice.

“Mrs. Mujuru told herself that she was now No. 2 in the party and in government and asked herself if it would not be possible for her to take the No. 1 job,” Mr. Mugabe said at a recent rally at which he lashed out at the Mujurus.

Her husband, though, was more outspoken. Perhaps because of the role he had played in securing Mr. Mugabe’s leadership, Mr. Mujuru was known as the only insider who challenged Mr. Mugabe during high-level meetings. For what he said was the good of the country and the economy, he pressed Mr. Mugabe to groom a successor and retire.

In 2008, Mr. Mujuru supported a new party, Mavambo, in an indirect move to weaken Mr. Mugabe.

“He wanted Mavambo as a mere lever to force Mugabe to stand down,” said Ibbo Mandaza, an academic and businessman who was one of the party’s founders.

Three years later, Ms. Mujuru got a phone call in the middle of an August night. Her husband had been found dead in their farmhouse an hour south of the capital, Harare.

When she arrived, the body was still burning with a blue flame, a sign that an accelerant had been used, she said. Her workers used a shovel to scrape the body off a carpet.

Later, at the morgue, the president came to offer his condolences on his way to the airport, she said.

Mr. Mugabe’s government pronounced the death an accident and later rejected Ms. Mujuru’s call for a second, independent autopsy. A spokesman for Mr. Mugabe’s party, Simon Khaya Moyo, said he “had no knowledge at all” about Ms. Mujuru’s assertions that forces close to Mr. Mugabe were responsible for her husband’s death.

“Let her speak for herself,” Mr. Moyo said. “She knows what to do next if she has correct information.”

But Ms. Mujuru said she had chosen to remain quiet, dutifully serving as Mr. Mugabe’s vice president until the first lady pushed her out in 2014.

“I wanted to change things from within, not just for myself but for the country,” she said.

Using a comparison she often makes, she said she saw herself as Deng Xiaoping, the leader who modernized China after the death of Mao Zedong.

Dewa Mavhinga, a researcher on Zimbabwe for Human Rights Watch, the advocacy group, said that unlike ZANU-PF hard-liners, Ms. Mujuru never called for political violence. She was considered open to working with the opposition and Western governments.

“That’s partly why she became a target,” Mr. Mavhinga said.

But Rashid Mahiya, the executive director of Heal Zimbabwe, a human rights group, said Ms. Mujuru was one of the biggest beneficiaries of ZANU-PF’s system of patronage and its widespread use of political violence. She, too, was rewriting history, exaggerating her reformist credentials, he said.

“We want her to come clean with her past,” Mr. Mahiya said. “The ZANU-PF color and paint that she is associated with does not go away.”

Ms. Mujuru said she was sorry about ZANU-PF’s use of violence, contending that she had always been “uncomfortable” with it and wished “she had said more” against it.

“It’s better I’m here with them,” she said of Mr. Mugabe’s opponents. “I’m sorry that could not have been enough to them. But, anyway, here I am.”